Syndiotactic 1,2-polybutadiene (SPBD) is a thermoplastic resin which can be utilized in making films, fibers and molded articles. For example, U.S. Pat. Nos. 4,394,473 and 4,957,970 disclose the use of SPBD in making bags and packaging. It can also be blended into elastomers, such as polydiene rubbers. Because SPBD contains double bonds which are attached in an alternating fashion to its backbone, it can be cocured with the rubbers in such blends. In fact, SPBD/rubber blends provide a unique combination of properties which make them useful in various tire compounds.
U.S. Pat. No. 4,790,365 discloses that incorporation of SPBD into rubber compositions which are utilized in the supporting carcass or innerliner of tires greatly improves the green strength of those compositions. Electron beam precure (microwave precure) is a technique which has gained wide commercial acceptance as a means of improving the green strength of synthetic elastomers which are used in building tires. However, electron beam precure techniques are costly. The incorporation of SPBD into blends of such synthetic elastomers can often improve green strength to the degree that electron beam precure is not required. The incorporation of SPBD into halogenated butyl rubbers which are utilized as the innerliner compositions for tires also greatly improves the scorch safety of such compositions. U.S. Pat. No. 4,274,462 disclosed that pneumatic tires having improved resistance against heat buildup can be prepared by utilizing SPBD fibers in their tread base rubber.
According to U.S. Pat. No. 4,790,365, the SPBD utilized in making the supporting carcass for tires has a melting point which is within the range of 120.degree. C. to 190.degree. C. and that it is preferred for the SPBD utilized in making the supporting carcass to have a melting point which is within the range of 150.degree. C. to 165.degree. C. The SPBD utilized in making tire innerliners has a melting point which is within the range of 120.degree. C. to 160.degree. C. and preferably has a melting point which is within the range of 125.degree. C. to 150.degree. C. The melting points referred to herein are minimum endotherm values determined from DSC (differential scanning calorimetry) curves.
Techniques for preparing SPBD by polymerizing 1,3-butadiene monomer are well known in the art. These techniques include solution polymerization, suspension polymerization and emulsion polymerization. The SPBD made utilizing these techniques typically have a melting point within the range of about 195.degree. C. to about 215.degree. C. It is accordingly necessary to reduce the melting point of the SPBD to render it suitable for utilization in some applications.
A process is disclosed in U.S. Pat. No. 3,778,424 for the preparation of syndiotactic 1,2-polybutadiene which comprises polymerizing 1,3-butadiene in an organic solvent in the presence of a catalyst composition composed of:
(a) a cobalt compound, PA1 (b) an organoaluminum compound of the formula AlR.sub.3, in which R is a hydrocarbon radical of 1-6 carbons and PA1 (c) carbon disulfide. PA1 (a) preparing a catalyst component solution by dissolving, in an inert organic solvent containing 1,3-butadiene, a cobalt compound, soluble in the organic solvent, such as (i) cobalt-.beta.-diketone complex, (ii) cobalt-.beta.-keto acid ester complex, (iii) cobalt salt of organic carboxylic acid and (iv) halogenated cobalt-ligand compound complex and an organoaluminum compound, PA1 (b) preparing a catalyst composition by mixing the catalyst component solution (prepared in step a) with an alcohol, ketone or aldehyde compound and carbon disulfide, PA1 (c) providing a polymerization mixture containing desired amounts of 1,3-butadiene, the catalyst composition and an inert organic solvent and PA1 (d) polymerizing 1,3-butadiene at a temperature which is within the range of -20.degree. C. to 90.degree. C. PA1 (A) preparing a catalyst component solution by dissolving, in an inert organic solvent containing 1,3-butadiene (a) at least one cobalt compound selected from the group consisting of (i) .beta.-diketone complexes of cobalt, (ii) .beta.-keto acid ester complexes of cobalt, (iii) cobalt salts of organic carboxylic acids having 6 to 15 carbon atoms and (iv) complexes of halogenated cobalt compounds of the formula CoX.sub.n, wherein X represents a halogen atom and n represents 2 or 3, with an organic compound selected from the group consisting of tertiary amine alcohols, tertiary phosphines, ketones and N,N-dialkylamides and (b) at least one organoaluminum compound of the formula AlR.sub.3, wherein R represents a hydrocarbon radical of 1 to 6 carbon atoms; PA1 (B) preparing a reaction mixture by mixing said catalyst component solution with a 1,3-butadiene/water mixture containing desired amounts of said 1,3-butadiene; PA1 (C) preparing a polymerization mixture by mixing carbon disulfide throughout said reaction mixture and PA1 (D) polymerizing said 1,3-butadiene in said polymerization mixture into polybutadiene while agitating said polymerization mixture. PA1 wherein R.sup.1 represents --OH, ##STR2## PA1 wherein R.sup.1 represents --OH, ##STR4## PA1 (a) 4-(alkylamino)benzaldehydes, PA1 (b) 4-(dialkylamino)benzaldehydes, PA1 (c) 2,4-di-(alkoxy)benzaldehydes, PA1 (d) 2,6-di-(alkoxy)benzaldehydes, PA1 (e) 2,4,6-tri-(alkoxy)benzaldehydes and PA1 (f) 4-(1-azacycloalkyl)benzaldehydes. PA1 wherein R represents an alkyl group containing from about 1 to about 20 carbon atoms. It is preferred for such alkyl groups to contain from 4 to 8 carbon atoms. PA1 wherein R and R' can be the same or different and are alkyl groups which contain from 1 to 20 carbon atoms. It is preferred for R and R' to be alkyl groups which contain from 1 to about 8 carbon atoms. PA1 wherein R and R' can be the same or different and represent alkyl groups which contain from 1 to 20 carbon atoms. It is preferred for R and R' to represent alkyl groups which contain from 1 to 8 carbon atoms. PA1 wherein R and R' can be the same or different and represent alkyl groups which contain from 1 to 20 carbon atoms. It is preferred for R and R' to represent alkyl groups which contain from 1 to 8 carbon atoms. PA1 wherein R, R' and R" can be the same or different and represent alkyl groups containing from 1 to 20 carbon atoms. It is preferred for R, R' and R" to represent alkyl groups which contain from 1 to 8 carbon atoms. PA1 wherein n is an integer from 3 to about 8. It is preferred for n to be an integer from 4 to 6. In other words, it is preferred for the 4-(1-azacycloalkyl)benzaldehyde to be selected from the group consisting of PA1 wherein R.sup.1 represents --OH, ##STR13## PA1 wherein R.sup.1 and R.sup.4, which are the same as or different from one another, are an alkyl radical of 1 to 6 carbon atoms and R.sup.2 and R.sup.3, which are the same as or different from one another, are a hydrogen atom or an alkyl radical having 1 to 6 carbon atoms. This type of .beta.-diketone complex of cobalt may be cobalt (ii) acetylacetonate or cobalt (iii) acetylacetonate. PA1 wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same as defined above. This type of cobalt complex may be a cobalt-acetoacetic acid ethyl ester complex. PA1 wherein R represents an alkyl group containing from 8 to 18 carbon atoms and preferably wherein R represents an alkyl group containing from 10 to 13 carbon atoms. The fatty alcohol sulfates which can be utilized normally have the structural formula: EQU R--O--SO.sub.3 Na PA1 wherein R represents an alkyl group containing from 6 to 28 carbon atoms and preferably wherein R represents an alkyl group containing from 11 to 17 carbon atoms. The oxo-alcohol ether sulfates which can be utilized generally have the structural formula: ##STR17## PA1 wherein R is an alkyl group having from 1 to 20 carbon atoms; alkylaryl sulfonates in which the alkyl groups contain preferably from 10 to 20 carbon atoms, e.g. dodecylbenzenesulfonates, such as sodium dodecylbenzene sulfonate; alkyl phenol sulfonates; sulfonic acids and their salts such as acids with the formula RSO.sub.3 Na, wherein R is an alkyl and the like; sulfonamides; sulfamido methylenesulfonic acids; rosin acids and their soaps; sulfonated derivatives of rosin and rosin oil; and lignin sulfonates, and the like.
U.S. Pat. No. 3,901,868 reveals a process for producing a butadiene polymer consisting essentially of syndiotactic 1,2-polybutadiene by the successive steps of:
U.S. Pat. No. 3,901,868 indicates that the melting point of the SPBD produced varies in response to the proportion of alcohol, ketone or aldehyde in the polymerization mixture. U.S. Pat. No. 4,153,767 shows that amide compounds, such as N,N-dimethylformamide, can be used in solution polymerizations to reduce the melting point of SPBD being synthesized.
U.S. Pat. No. 4,429,085 discloses a process for producing syndiotactic 1,2-polybutadiene by suspension polymerization in an aqueous medium. In this aqueous polymerization process, polybutadiene which has an essentially syndiotactic 1,2-microstructure is made by the steps of:
U.S. Pat. No. 4,751,275 discloses a process for the preparation of SPBD by the solution polymerization of 1,3-butadiene in a hydrocarbon polymerization medium, such as benzene, toluene, cyclohexane or n-hexane. The catalyst system used in this solution polymerization contains a chromium-III compound which is soluble in hydrocarbons, a trialkylaluminum compound and a dialkylphosphite, such as di-neopentylphosphite or di-butylphosphite.
U.S. Pat. No. 4,902,741 and U.S. Pat. No. 5,021,381 disclose a process for preparing a syndiotactic 1,2-polybutadiene latex by emulsion polymerization which comprises polymerizing 1,3-butadiene monomer in an aqueous reaction mixture which is comprised of (1) water, (2) at least one emulsifier, (3) 1,3-butadiene monomer, (4) a catalyst emulsion composition which is prepared by dissolving in an inert organic solvent containing at least one polyene (a) at least one cobalt compound selected from the group consisting of (i) .beta.-ketone complexes of cobalt, (ii) .beta.-keto acid ester complexes of cobalt, (iii) cobalt salts of organic carboxylic acids having 6 to 15 carbon atoms and (iv) complexes of halogenated cobalt compounds of the formula CoX.sub.n, wherein X represents a halogen atom and n represents 2 or 3, with an organic compound selected from the group consisting of tertiary amine alcohols, tertiary phosphines, ketones and N,N-dialkylamides and (b) at least one organoaluminum compound of the formula AlR.sub.3 wherein R represents a hydrocarbon radical of 1 to 6 carbon atoms to produce a catalyst component solution, and microfluidizing the catalyst component solution with an oil, a surfactant and water to an average particle size which is within the range of about 10 nanometers to about 1000 nanometers and (5) at least one member selected from the group consisting of carbon disulfide and phenyl isothiocyanate.
The synthesis of SPBD in an aqueous medium offers several important advantages over solution polymerizations. Water, as a medium in which to carry out such a polymerization, is less expensive, more easily purified and has a higher heat capacity. Conducting such polymerizations in an aqueous medium also permits for higher monomer and higher solids concentrations because of the lower viscosity of a polymer suspension or emulsion compared with that of a polymer solution. The main drawback associated with aqueous suspension and emulsion polymerizations for producing SPBD is the difficulty associated with reducing the melting point of the SPBD. In other words, it is difficult to control the chemical structure and hence the crystallinity and melting point of SPBD which is synthesized in an aqueous medium. Even though numerous modifiers can be used to reduce the level of crystallinity and resulting melting point of SPBD which is synthesized in solution, there are few efficient modifiers for reducing the crystallinity of SPBD which is synthesized in an aqueous medium.
U.S. Pat. No. 5,011,896 discloses the use of 4-(alkylamino)benzaldehydes, 4-(dialkylamino)benzaldehydes, 2,4-di-(alkoxy)benzaldehydes, 2,6-di-(alkoxy)benzaldehydes, 2,4,6-tri-(alkoxy)benzaldehydes and 4-(1-azacycloalkyl)benzaldehydes as modifiers for reducing the melting point of SPBD which is synthesized in an aqueous medium. U.S. Pat. No. 5,405,816 discloses the utilization of N,N-dibutylformamide as a highly effective modifier for reducing the melting point of SPBD synthesized in such polymerizations.